hdu1754 单点更新

第二道线段树，哈哈哈，已经从区间求和萌萌哒变成求最大值，我是不是好无聊哦~~~~

代码：

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cstdlib>
 4 #include <iostream>
 5 #include <algorithm>
 6
 7 using namespace std;
 8
 9 const int maxn = 200000 + 10;
10 int a[maxn];
11 struct node
12 {
13     int l, r, v;
14
15 } va[maxn<<2];
16
17 void build(int l, int r, int i)
18 {
19     va[i].l = l;
20     va[i].r = r;
21     int m = (l + r)/2;
22     if(l == r) {
23         va[i].v = a[l];
24         return ;
25     }
26     build(l, m, i<<1);
27     build(m+1, r, i<<1|1);
28     va[i].v = max(va[i<<1].v, va[i<<1|1].v);
29 }
30
31 void Update(int id, int num, int i)
32 {
33     if(va[i].l == va[i].r) {
34         va[i].v = num;
35         return ;
36     }
37     else {
38         if(id <= va[i<<1].r) Update(id, num, i<<1);
39         else Update(id, num, i<<1|1);
40     }
41     va[i].v = max(va[i<<1].v, va[i<<1|1].v);
42 }
43
44 int Quary(int l, int r, int i)
45 {
46     int m = (va[i].l + va[i].r)/2;
47     if(l == va[i].l && r == va[i].r) {
48         return va[i].v;
49     }
50     if(r <= m) return Quary(l, r, i<<1);
51     else if(l > m) return Quary(l, r, i<<1|1);
52     else return max(Quary(l, m, i<<1), Quary(m+1, r, i<<1|1));
53 }
54 int main()
55 {
56     //freopen("test.in", "r", stdin);
57     char s[5];
58     int N, M, x, y;
59     while(scanf("%d%d", &N, &M) != EOF) {
60         for(int i = 1; i <= N; i++) {
61             scanf("%d", &a[i]);
62         }
63         build(1, N, 1);
64         while(M--) {
65             scanf("%s %d %d", s, &x, &y);
66             if(s[0] == ‘Q‘) printf("%d\n", Quary(x, y, 1));
67             else Update(x, y, 1);
68         }
69     }
70     return 0;
71 }

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